Making headway … Women and children in Madagascar, one of the least developed countries. Inclusiveness is on the OECD forum agenda. Photograph: Reuters

International support is critical for the world's poorest countries to make progress on the millennium development goals (MDGs), said a UN representative on Thursday, 1,000 days before the MDG target date.

Gyan Chandra Acharya, the UN undersecretary general for the least developed countries (LDCs), acknowledged the progress made in reducing the number of people living in extreme poverty since the MDGs were set in 2000. But he pointed out that about half of people in the LDCs – the world's poorest 49 countries – still lived below $1.25 a day, the World Bank's measure of extreme poverty.

"The capacity of the state is very limited," said Acharya at an OECD global forum on development in Paris, looking at the framework for when the MDGs expire in 2015. "We must make sure that the unfinished agenda is taken care of … there is no way they can do it themselves."

Yet the latest OECD figures will concern Acharya, since they show a noticeable shift in aid away from the poorest countries and towards middle-income countries. The shift benefited countries such as China, India, Indonesia, Pakistan, Sri Lanka, Uzbekistan and Vietnam. By contrast, aid is likely to stagnate to countries with the largest MDG gaps and poverty levels, including sub-Saharan African countries such as Burundi, Chad, Madagascar, Malawi and Niger.

Acharya argued that no matter how great the resources these LDCs can mobilise, they will still need international support in a focused manner. Noting that the poorest in the LDCs lived in rural areas – about 70% – he suggested, as many have done, that the post-2015 framework make inclusive economic growth one of its pillars. Inclusiveness was also a prominent theme in last week's UN high-level panel meeting in the Indonesian province Bali.

Acharya called for aid to focus on infrastructure, access to energy, and sustainable agriculture.

Earlier, Olusegun Obasanjo, the former Nigeria president, spoke of the importance of international targets in helping to frame national development policy, although he provided cautionary tales about "one size fits all" prescriptions by the International Monetary Fund and the World Bank, particularly structural adjustment programmes.

As an example of how the MDGs helped Nigeria, Obasanjo said he persuaded creditors to ease their loan conditions by arguing that debt relief would help his country to make progress on education.

"I wanted to reduce the debt profile of Nigeria," he told the audience. "One argument I used to convince creditors was to say that the money saved from debt reduction would be channelled towards the MDGs … Targets set by international organisations are definitely very helpful in formulating our own policies and in getting donor agencies to buy in to what we were doing."

Looking beyond 2015, Obasanjo expressed particular concern about Africa's youth bulge. Giving the young skills and jobs was crucial, he said – otherwise the continent faced the threat of social instability, along the lines of the Arab spring. "We are sitting on a keg of gunpowder," said Obasanjo, describing the problem of youth underemployment and unemployment.

Corruption, education and environment completed the list of priorities for Obasanjo.

Abdalla Hamdok, the deputy executive secretary of the UN economic commission for Africa, raised the issue of illicit flows, a subject David Cameron wants to focus on as president of the G8 group of industrialised countries, which is holding a June summit in Northern Ireland. But that would mean dealing with UK-administered territories such as the British Virgin Islands.

"We cannot resolve this problem on our own," said Hamdok. "You can imagine the impact on the MDGs if we can capture these illicit flows."